A rotary milling tool is formed as a disk or cylindrical body whose rotation axis is parallel to the rotation axis of the workpiece. Cutting tools carried on the periphery or outer surface of the disk or cylinder perform successive necessary cutting operations on the workpiece, the rotary milling tool also being outfitted with different cutting inserts for different machining purposes, such as coarse and fine machining.
The main application of the method according to the invention is predominantly in the automobile and utility vehicle industry, there in particular in the machining of the main and pin bearings of crankshafts, cam shafts, flywheel gears, and axles.
In order to machine a cast crankshaft blank the actual crankshaft is mounted at both ends in chucks of a machine equipped with respective main spindles. The main spindles are driven by two synchronously running multiphase motors. In order to be able to machine both the main bearings as well as the pin bearings, which are axially offset from one another, the chucks of the machine are vertically adjustable in their holders. According to the number of main or pin bearings to machine, according to the prior art rotary milling tools are moved by means of supports radially toward the respective bearings until the cutting inserts mounted on the periphery or outer surface of the rotary milling tool enter into contact with the parts of the workpiece to be machined. In order to be able to machine the pin bearings which are eccentric to the crankshaft axis over their entire cylindrical outer surfaces, it is necessary to move the rotation axis of the rotary milling tool in a circular arc. The simultaneous machining of two or more pin bearings by a corresponding number of rotary-milling tools is no problem with respect to setting of the tool advance and the respective rotary rotation rate of the workpiece and of the rotary-milling tools since similar cutting operations can be carried out parallel next to one another. The same is true for the simultaneous machining of main bearings or the simultaneous machining of cheeks, counterweights, or other similar parts of the workpiece. The cutting inserts on the respective rotary-milling tools are very greatly stressed with such operations so that as a rule one can count on a generally similar long service life of all the rotary milling tools that are used for the same cutting operations.
Different relationships exist however when simultaneously different workpiece parts, for example crankshaft parts such as for example cheeks on the one hand and main bearings on the other are being machined. A constant workpiece rotation speed has the disadvantage that it is only optimized for one cutting operation, for example machining of the main bearings. In addition the actual arc length for workpiece parts such as cheeks vary considerably due to their lack of rotation symmetry.